Rocket motor extendible nozzle exit cone

ABSTRACT

A membrane of refractory material having opposed arcuate edges one of which is longer than the other, having opposed straight edges which when welded together in edge-to-edge relationship form the frustum of cone, is deformed by brake or die press means over a portion adjacent the longer arcuate edge to provide thereon a pattern comprising two sets of creases in each of five equal sectors, a first set of which creases points at the viewer from the exterior of the membrane (as it subsequently is formed into the frustum of a cone) and a second set which points away from the viewer. The creases of the first set run both circumferentially and longitudinally with respect to the surface of the cone while the creases of the second set run longitudinally only. This crease pattern enables a membrane portion forward of the larger diameter of the cone to be folded inwardly in multiple layers and permits an amount of membrane material sufficient to produce a very large area ratio at the exit plane to be stowed in a much reduced envelope, with the cone in folded form being quite rigid. 
     In other embodiments the membrane is formed into an integral seamless free standing shape by spinning a sheet blank against a mandrel and by condensing or electroplating a thin coating of a refractory material on a substrate or mandrel.

This is a divisional of co-pending application Ser. No. 876,570 filedJune 20, 1986, now U.S. Pat. No. 4,766,657, which iscontinuation-in-part of application Ser. No. 762,472, filed Aug. 5,1985, now abandoned.

1. Field of the Invention

The present invention relates to an improvement in an extendible nozzleexit cone for rocket motors that are designed for operation at vacuum ornear vacuum conditions.

2. Description of the Prior Art

Deep space ballistic missile systems or satellite probes require highperformance, low weight, and highly packageable primary propulsionsystems. Excluding propellant tanks, the largest component of thepropulsion system is the rocket motor exhaust nozzle. The rocket motornozzle takes up a large amount of valuable space relative to its mass.

The exit cone of a conventional nozzle for rocket motors is designed foroptimum performance at the median altitude of the intended trajectory.One of the functions of the exit cone is to provide an inclined surfaceagainst which the expanding exhaust plume of the rocket motor can bear,thereby to provide some of the forward thrust of the rocket motor. Theexhaust plume grows larger with increasing altitude of the rocket motorbecause of the lower pressures of the ambient atmosphere at the higheraltitudes. At low altitudes, the exhaust plume is too small for theavailable surface of the exit cone. As a result, a partial vacuum tendsto form on the inside edges of the exit cone, thereby creating anatmospheric drag on the rocket. At high altitudes, the exhaust plume istoo large for the exit cone so that much of the potential energy isunused. A rocket motor nozzle that is sufficiently large to make fulluse of the expanding exhaust gases of a rocket motor in the lowpressures existing at high altitudes would normally occupy aninordinately large proportion of the available storage space in silos,submarines, and between stages of a multiple-stage missile.

Various proposals have been made in the prior art to provide a largeexpansion ratio nozzle that can be stowed in a configuration of reducedlength and thereby made to fit in a minimal space, and that can beextended to a configuration suitable for high altitude operation aftermotor ignition and lift off. These have included the use of:

(a) a rocket motor nozzle extension cone or skirt that is folded in asingle layer inwardly and forwardly of the rocket motor nozzle when in astowed position, and is actuated, that is, deployed to a fully extendedposition by foward-to-aft flow of rocket motor gas, as disclosed in U.S.Pat. No. 3,358,933 to J. H. Altseimer, and in U.S. Pat. No. 4,272,956 toG. C. Lamere et al.;

(b) an inflatable rocket motor extension cone or skirt that is foldedforwardly of, that is back around the rocket motor nozzle, exteriorlythereof, and later inflated by rocket motor gas to achieve a desiredfrusto conical shape aft of the rocket motor nozzle, as in U.S. Pat. No.3,596,465 to T. O. Paine et al.;

(c) a rocket motor extension cone or skirt that is folded forwardly of,that is, back around the motor nozzle, exteriorly thereof, and includinga cover assembly attached to the aft or exit end of the skirt that sealsthe extension cone, and upon motor operation, seals the gas pressuretherein sufficient to cause the skirt to unroll into its extendedconfiguration, as in U.S. Pat. No. 3,711,027 to L. F. Carey and U.S.Pat. No. 3,784,109 to J. W. Dueringer;

(d) a rocket motor extension cone that is folded forwardly of, that is,back around the motor nozzle, exteriorly thereof, and including aplurality of mechanical actuators for causing the skirt to unroll intoits extended configuration, as in U.S. Pat. No. 3,346,186 to D. L.Fulton et al., U.S. Pat. Nos. 4,125,224, 4,162,040, 4,184,238 and4,387,564 to L. F. Carey, U.S. Pat. No. 4,213,566 to L. E. Miltenberger,and U.S. Pat. Nos. 4,383,407 and 4,489,889 to F. S. Inman;

(e) a rocket motor extension cone as described in item (d) furtherincluding a skirt attached to the aft end of the extension cone that isflared toward the interior of the extension cone when the latter is inits stowed position and is actuated into its extended configuration by aforward-to-aft flow of rocket motor gas, as in U.S. Pat. Nos. 4,125,244,4,162,040, 4,184,238, and 4,387,564 to L. F. Carey.

There are problems with the prior art proposals for providing highperformance over the entire range of intended trajectory in that theyare deficient in meeting the large expansion ratios required for highaltitude rocket flight while still remaining within length, weight andeconomic limiting constraints.

Thus, with respect to the prior art mentioned in item (a) above, whichprior art is schematically represented by FIG. 1 of the drawings, it isevident that since the length Ls along the straight meridian of theextended cone portion 1 of a rigid cone 2 cannot exceed the radiusR_(f), the exit opening of cone 2, the length L_(a) along thelongitudinal axis 3 of the cone extension 1 must be smaller than L_(s).This seriously limits the expansion ratio that is obtainable by theprior art of item (a) since the length L_(s) must be short enough to fitwithin cone 2 in its stowed condition.

The prior art of item (b) involves the use of an inflatable extensioncone consisting of two woven stainless steel interconnected panels andincluding a manifold connection for dumping rocket motor gas between thepanels for inflating the cone. The double panel and manifold connectionboth add undesirably to the weight, bulk and complexity of theconstruction.

With respect to the prior art of item (c), the requirement for the coverassembly that is attached to the exit end of the extension skirt addsundesirably to the weight of the extension cone, the transverse loadthereon, and the complexity of the construction.

The prior art of items (d) and (e) involve the use of mechanicalactuators such as pneumatic cylinders that add undesirably to theweight, bulk and complexity of the construction.

The present invention is concerned particularly with a form ofextendible rocket motor exit cone in which the nozzle extension isfolded inwardly of itself and is characterized in its provisions forpermitting the straight meridian corresponding to L_(s) of the prior artrepresentation of FIG. 1 to be much larger than R_(f) or even largerthan R_(e), the radius at the exit plane of the cone extension 1. Thisallows a sufficient amount of membrane material for the cone extensionto produce a very large area ratio at the exit plane to be stowed withsubstantially increased rigidity in a much reduced envelope incomparison with the prior art, and in making possible the use ofthinner, and hence, lighter exit cone extension membranes.

SUMMARY OF THE INVENTION

An object of the invention is to provide an improved method for makingan extendible rocket motor exit cone having a very large area ratio froma membrane of refractory metal or other heat resistant material, whichextendible exit cone may be collapsed by folding for stowage and thedeployment of which lends itself to induction by a forward-to-aft gasflow therein upon motor operation.

A further object of the invention is to provide a method of folding asheet stock (metal, etc.) development of cut arcuate membrane in theform of a cone or conical frustum, with a straight meridian, in such amanner that the aft or larger diameter region of the cone that isconstructed by attaching the opposed ends in edge-to-edge relationshipmay be collapsed for stowage with vastly reduced overall length, minimumdiameter, and with substantially increased rigidity in comparison withthe fully deployed unit, and more particularly, wherein, in the stowedcondition, the material comprising the aft portion of the membrane issituated in multiple layers within the forward portion so thatdeployment may be induced by forward-to-aft gas flow within the cone.

Another object of the invention is to provide such an improved methodfor making an extendible nozzle exit cone which is characterized in thatin collapsing the cone, for stowage, the membrane of the extendiblenozzle exit cone is folded inwardly thereof, with multiple folds, fromthe aft end.

Still another object of the invention is to provide an improved method.for making an extendible nozzle exit cone from very thin membranes whichis characterized in that, in the stowed form, the extendible nozzle exitcone is quite rigid.

A further object of the invention is to provide an improved extendiblenozzle exit cone for rocket motors in which the extendible nozzle exitcone is folded inwardly thereof, with multiple folds, from the aft endthereby permitting a sufficient amount of membrane material for thenozzle extension to produce a very large area ratio at the exit plane tobe stowed in a much reduced envelope, with the extendible exit cone instowed form being quite rigid.

Another object of the invention is to provide a method of fabricatingsuch an improved extendible nozzle exit cone for rocket motors from aflat sheet or membrane of refractory metal or other material using aspinning technique involving a conical mandrel or substrate and acombination of rotation and force.

Further objects of the invention are to provide such an improved nozzleexit cone for rocket motors using chemical vapor deposition orelectroforming or electrodeposition or plasma deposition techniques,with or without intentional variations in membrane thickness.

Still another object of the invention is to provide an improved methodof fabricating such an improved extendible nozzle exit cone for rocketmotors that facilitates alteration in the basic configuration so thatregions between or beyond approximately circumferential fold lines mayhave cone angles somewhat different from one another.

In accomplishing these and other objectives, the invention, in oneembodiment, comprises a system of creasing and folding a sheet stock(metal, etc.) development of a cut arcuate membrane in the form of acone or conical frustum, with a straight meridian, in such a manner thatthe aft or larger diameter region of the cone that is constructed byjoining the two opposed straight edges may be collapsed for stowage withvastly reduced overall length, maximum diameter, and with substantiallyincreased rigidity in comparison with the fully deployed unit.

The improved extendible nozzle exit cone in another embodiment of theinvention is formed as an integral, seamless, free-standing shape from aflat circular sheet or disc of refractory metal or other membranematerial by a spinning method involving a combination of rotation andforce. Specifically, the disc is progressively forced against a conicalcharacterized mandrel, starting at the smaller diameter thereof, bymeans of one or more small rollers that are advanced, radiallyoutwardly, toward the larger diameter.

In still another embodiment of the invention, the membrane of theimproved extendible nozzle exit cone is fabricated of refractory metalor other material as an integral, seamless, free-standing shape by achemical vapor deposition technique involving the flowing andcondensation of gaseous elements or compounds over or within a heatedconical substrate or mandrel. Thermal decomposition or reduction of themetallic ion of the gaseous medium results in deposition of therefractory metal onto or within the mandrel.

The membrane of the improved extendible nozzle exit cone of a furtherembodiment of the invention is formed as an integral, seamless,free-standing shape by electroforming (electrodeposition) or by plasmadeposition of the refractory metal or other material on or within asubstrate or mandrel.

In each of the embodiments emphasizing deposition on or within on amandrel, the mandrel may be characterized in having formed narrow ridgesand grooves in the surface thereof in the region of larger diameter, asrequired, for the formation of crease lines in the formed conicalmembrane that are necessary for enabling the inward folding of thelatter in multiple layers. In each case, removal of the mandrel resultsin the desired extendible nozzle exit cone.

The material comprising the aft portion of the cone in the stowedcondition, in each of the embodiments of the invention, is situated inmultiple layers within a forward portion of the cone so that deploymentis readily induced by forward-to-aft gas flow from the rocket motorwithin the cone. The forward portion of the membrane need not beextensively folded, and for some purposes, it may be preferable not tofold it at all.

The various features of novelty which characterize the present inventionare pointed out with particularity in the claims annexed to and forminga part of this specification. For a better understanding of theinvention, its operating advantages, and specific objects attained byits use, reference is made to the accompanying drawings and descriptivematter in which preferred embodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic fragmented drawing illustrating certainrelationships of a prior art nozzle extension as mentioned hereinbefore;

FIG. 2 is a perspective view, with a portion shown in cross section, ofa rocket motor having an extendible nozzle exit cone according to anembodiment of the present invention, with the extendible nozzle exitcone shown in the stowed condition thereof;

FIGS. 3 through 6 show the extendible nozzle exit cone of FIG. 2 invarious stages of deployment thereof;

FIG. 7 is a view of the aft end of the extendible nozzle in its stowedcondition;

FIG. 8 is a view of a partial plan, specifically a fifth, of thedeveloped exterior surface of the extendible nozzle exit cone of FIGS. 2through 7;

FIG. 9 is a fragmentary perspective view showing how a thin sheet metalworkpiece may be positioned upon the table of a brake press for havingfold or crease lines formed thereon;

FIG. 10 is a fragmentary perspective view showing, alternatively, how athin metal sheet may be placed upon a die plate and crease pressed toform the fold or crease lines thereon;

FIG. 11 is a fragmentary view illustrating the operation of the diepress of FIG. 10;

FIG. 12 illustrates a brake-pressed and cut thin arcuate sheet metalworkpiece that is obtained preliminary to further forming into theextendible nozzle exit cone of the invention;

FIG. 13 illustrates a manner of folding the membrane axi-symmetricallyat the several fold lines beginning with the aft end of the extendedcone in collapsing the aft end of the cone for stowage in a forwardportion thereof;

FIG. 14 is a schematic drawing illustrating certain relationships of theextendible nozzle exit cone according to the invention as contrastedwith corresponding relationships of the prior art illustrated in FIG. 1;

FIG. 15 is a fragmentary view illustrating a trapped supporting systemfor the extendible nozzle of the invention;

FIG. 16 is a drawing, partly in section, illustrating the formation ofan extendible nozzle exit cone according to another embodiment of theinvention by forcing a disc of refractory metal or other materialagainst a mandrel by means of a small roller;

FIG. 17 is a schematic drawing illustrating the formation of anextendible nozzle exit cone according to still another embodiment of theinvention by chemical vapor deposition of the refractory metal or othermaterial on a mandrel; and

FIG. 18 is a schematic drawing illustrating the formation of anextendible nozzle exit cone according to a further embodiment of theinvention by electrodeposition of a refractory metal or other materialon a characterized mandrel.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In accordance with the present invention, there are provided severalimproved methods for making an extendible nozzle exit cone forattachment to the exit end of a rocket motor nozzle. In one such method,a portion of the aft end of the cone is initially folded inwardly of aforward portion thereof for collapsing the cone for compact stowage. Theinwardly folded aft end is adapted to be unfolded, upon firing of therocket motor, due to the forward-to-aft flow of rocket motor gas throughthe extendible nozzle exit cone. Such extension of the extendible nozzleexit cone increases the ratio of the effective rocket motor extendiblenozzle exit plane area to the rocket motor nozzle throat area. Byfolding a portion only, for example two-thirds of the aft end within theforward end of the extendible exit cone in the collapsed conditionthereof, there is provided a larger exit plane area at firing of therocket motor for effecting a build up of sufficient pressure within thecone for fast and smooth unfolding, and hence, deployment of the cone toits extended position

The method of the present invention, in one embodiment, comprisesseveral steps including cutting a workpiece of heat-resistant ductilematerial, as described hereinafter, into plan view arcuate form ofappropriate size, as illustrated in FIG. 12 with opposed straight endsthat may be brought into edge-to-edge relationship to form a frustum ofa cone. The arcuate form of the workpiece is so selected that thesmaller radius or arcuate end or edge of the frustum of a cone issuitable for attachment to the exit end of the rocket motor nozzle andthe larger radius or arcuate end or edge of which is of such size as toprovide the desired increase in area ratio.

Following the step of cutting the arcuate shaped workpiece of thinheat-resistant material, the workpiece is deformed over a portionadjacent the longer arcuate edge to provide thereon a pattern comprisingtwo sets of folds or creases in each of five substantially equal sectorsinto which the workpiece is divided, a first set of which creases pointsat the viewer from the exterior of the workpiece (as it subsequently isformed into the frustum of a cone), and a second set which points awayfrom the viewer. The two sets of creases are so formed on the surface ofthe workpiece and in such relation with each other that when the opposedstraight ends of the arcuate workpiece are attached to each other toform a frustum of a cone, the aft end of the cone is adapted for foldinginwardly into a portion of the forward end in a plurality of inwardlyfolded layers. While the workpiece is described as being divided intofive sectors, it will be understood that many more sectors than five,all of equal size, may be provided, if desired. A minimum of foursectors is necessary, however, for the folding and unfolding of themembrane to be feasible.

Further steps in this method of the making of the extendible nozzle exitcone of the present invention, according to this embodiment, includeattaching the opposed straight ends of the arcuate workpiece inedge-to-edge relationship as by a single weld to form a frustum of acone followed by axi-symmetric folding inwardly and forwardly, as byhand, a portion of the surface forward of the larger diameter or aft endof the cone in a plurality of inward folds thereby to collapse the conefor compact stowage.

FIGS. 2 through 6 depict a particular version of an extendible nozzleexit cone 10, according to this embodiment of the invention, for arocket motor designated by the numeral 12. The cone 10 may be made, ashereinbefore described, by folding a flat sheet or membrane of suitablycut refractory metal or other heat and erosion resistant material.

By way of example and not limitation, it is noted that the nozzle 14 ofthe rocket motor 12 may have a throat 13 having a diameter of 3.85inches. The membrane designated 16, of the deployed or extendedextendible nozzle exit cone 10 may have a 17° half angle, and isattached in conventional and suitable manner (not shown) to the rocketmotor cone 14 of thicker material at a diameter in the 23 to 27 inchrange. The thicker cone 14 of smaller area ratio may have a half anglelarger than 17°.

On the extendible membrane exit cone 10, the area ratios are 256 at theexit plane 18 and 80.3 at a point of departure designated 20, from thegenerally conical form. At this intermediate location 20, the aft endview of the stowed configuration is pentagonal.

One-fifth of the developed surface of the cone, showing fold or creaselines and fold directions, is shown in FIG. 8.

FIG. 2 illustrates the fully stowed condition of the extendible exitcone 10. The overall reduction of length at the longitudinal axis 22 ofthe extendible cone 10, is about 115% of the exit plane radius, and morethan 200% of the deployed radius at the intermediate location 20. Thisis more than twice what has been accomplished in the prior art, asrepresented by FIG. 1. The free length of the conical membrane 16between where it clears the attachment to the rocket motor nozzle 14 andthe location 20 of the departure from generally conical form is about 16inches.

As those skilled in the art will understand, greater or lesserdeployed-to-stowed condition envelope reductions, and forms with largeror smaller exit plane area ratios, may be achieved through alterationsof the angular frequency, the number of approximately circumferentialfolds, and the distances between adjacent folds. In the fully stowedcondition, as shown in FIGS. 2 and 7, the folds at the aft end of theextendible cone 10 form a pyramid 24 with the apex thereof on thelongitudinal axis 22, which pyramid 24 closes the exit end of the cone10. This closure of cone 10 is sufficiently tight that upon initiationof operation or firing of the rocket motor 12, the resultingpressurization within the cone and forward-to-aft flow of gas causes thefolds of cone 10 to unfold and to deploy the cone 10 to its fullyextended condition in a smooth sequence of opening the successive foldsand layers.

FIG. 3 illustrates the situation as deployment begins. The approximatelyradial features or folds indicated at 26, which catch the gas asforward-to-aft flow begins, are clearly visible. Each side of theseradial features 26 is composed of a zone between the exit plane and thesecond approximately circumferential fold, indicated at 34, at midwidthof the one-fifth of full development region shown in FIG. 8. Each radialfeature 26 consists of two layers of membrane 16.

FIGS. 4 and 5 illustrate the approximately radial features 30 and 32,respectively, that continue to be exposed during deployment. Theseradial features 30 and 32 capture the gas which forces the continuationof unfolding and deployment. In FIG. 6, all that remains to beaccomplished for complete deployment is the development of a sufficientrate of flow of forward-to-aft gas within the membrane 16 of exit cone10 to force it to the stable circular form.

In most of the extendible exit cone 10 described in connection withFIGS. 2 through 6, three layers of the material of membrane 16 are incontact in the stowed condition. The triangular zones 36 between theexit plane 18 and first approximately circumferential fold indicated at28 and adjacent to the boundaries of the one-fifth of full developmentregion, as seen in FIGS. 6 and 8, form a small region where five layersof the material of membrane 16 are in contact in the stowed condition.

In the partial plan development of the exterior surface of theextendible exit cone 10, as shown in FIG. 8, fold lines are shown eitheras solid lines or dotted lines. Those shown solid have the apex thereofpointing toward the viewer. Those shown dotted have the apex pointingaway from the viewer.

In accordance with this embodiment of the invention, the pattern offolds or creases, as shown in FIG. 8, may be made in an appropriatelycut membrane 16 of arcuate shape forming a workpiece 44 by means of abrake press, as schematically illustrated in FIG. 9. A brake press is awell known device in the art and is widely used for bending andproducing shapes from ferrous and nonferrous metal sheets and plates.Particular advantages of a brake press are its versatility, the ease andspeed with which it can be changed from one set up to another, and lowcosts of tooling. A brake press is a slow speed punch press having along relatively narrow bed or table and a ram mounted between endhousings. The rams may be actuated mechanically or hydraulically.

For facilitating the brake press operation, it may be desirable to use aconventional brake press modified in a manner well known to thoseskilled in the art. Thus, there is a need to control the length of theedge on the table 40 of the brake press 38, as shown in FIG. 9, toaccommodate the several lengths of the different creases. Thus, it iscontemplated to modify the brake press 38 by the use of several tables40 each with an edge of the required length and which may besubstituted, one for another, in making the folds or creases in themembrane 16.

As those skilled in the art will understand, also, the pattern of foldsor creases may be formed in the membrane 16 by means of a die press 42,as shown in FIGS. 10 and 11, the membrane 16 being laid upon a die plateand crease-pressed. The die press 42 may be selected, as desired, tomake the required creases on both sides of the sheet or workpiece 44 ofmembrane 16, as shown in FIG. 12, in one die pressing operation, or onlyone-fifth thereof, as shown in FIG. 8, in each of five successive diepressing operations.

FIG. 12 illustrates a brake-pressed, or die pressed, and cut membranesheet or workpiece 44 showing the plurality of bends or creases thathave been formed in the membrane 16.

Following the brake pressing or die pressing operation, the opposedstraight ends 46 and 48 are attached to each other in any suitablemanner, as for example, by a single weld, to form the extendible exitcone 10.

By reference to FIGS. 8 and 12, it will be seen that the pattern ofcreases or folds that is formed on the workpiece 44 of FIG. 12, fromwhich cone 10 is formed, comprises spaced first, second and thirdapproximately circumferential fold or crease lines 28, 34 and 54,respectively. The first fold line 28 and the third fold line 54 extendcompletely across the width of the sector designated 60 shown in FIG. 8comprising one-fifth of the complete arcuate workpiece 44 shown in FIG.12. The second fold line 34 of sector 60 is comprised of two creaselines 62 and 64 that meet at an angle at a midpoint 66 on sector 60 andextend in opposite directions to respective midpoints of adjacentsectors that are identical to sector 60. While the lines or creases 28,54 and 34 (formed by creases 62 and 64) are straight, they formapproximately circumferential fold lines over the width of theworkpiece, as shown in FIG. 12. As shown, the three fold lines 28, 34,and 54 are approximately equidistant from each other with the first foldline 28 being substantially the same distance from the junction ofcrease lines 62 and 64 as from the longer arcuate outer edge 51 at theexit plane 18 of the sector 60. The smaller radius or shorter arcuateedge is designated 52.

The fold or crease lines 28, 54, 62 and 64, as shown in FIG. 8, compriseseveral of a first set of crease lines formed in the workpiece 44 inrespect of which the apex of the fold points at the viewer. Other creaselines of such first set of crease lines comprise a line 68 that connectsthe junction 66 of crease lines 62 and 64 to the midpoint 70 of foldline 28 and lines 72 and 74 that connect the junction 66 to a respectiveend of fold line 54. Still others of the crease lines of the first setof crease lines connect the midpoint 76 of the longest arcuate edge 51at the exit plane 18 of sector 60 to the ends and spaced intermediatepoints on the fold line 28. These are crease lines 78, 80, 82 and 84.Additional crease lines 86 and 88 connect a respective end of fold line28 to the longest arcuate edge 51 at the exit plane 18 of sector 60.

Crease lines of a second set of cease lines have an apex that point awayfrom the viewer. These include a crease line 90 that connects themidpoint 76 on the longest arcuate edge 51 at the exit plane 18 ofsector 60 and the midpoint 70 on the first fold line 28. Other suchcrease lines include lines 92, 94, 96 and 98 that connect the midpoint66 of the second fold line 34 to the ends and intermediate points on thefirst fold line 28. Crease lines 100 and 102 connect one end of foldline 28 to the longest arcuate edge 51 at the exit plane 18 of sector 60and crease lines 104 and 106 connect the other end of fold line 28thereto.

When workpiece 44 is formed into a frustum of a cone, crease lines ofthe first set run both circumferentially and longitudinally with respectto the surface of the cone, as may be seen by reference to FIGS. 8, 12and 13. Thus, crease lines 28, 34 and 54, which are shown in full lines,run circumferentially and crease lines 68, 86 and 88, also shown in fulllines, run longitudinally with respect to the conical surface. Thecrease lines of the second set on the other hand, run longitudinallyonly with respect to the surface of the cone. These are lines 90, 92,94, 96, 98, 100, 102, 104, 106, 108 and 110, all of which are showndotted.

In summary, crease lines of the first set run both circumferentially andlongitudinally with respect to the surface of the cone 10, as seen inFIG. 13, and crease lines of the second set run longitudinally only withrespect to that surface.

FIG. 13 illustrates how the membrane workpiece of FIG. 12, when formedinto exit cone 10, may be folded inwardly upon itself progressively andaxi-symmetrically from the aft end to the point of departure 20 on theforward end whereby to place the extendible cone 10 in the stowedcondition thereof. Such folding may be done by hand.

The folds for initiating the inward folding of the extended cone 10about the approximately circumferential fold line 28 have been indicatedin FIGS. 12 and 13 by the letters A through E. Alternate ones of thefolds, for example, folds A, C, E, B and D are pinched, in turn, fromthe outer surface of the membrane 16. Specifically, pinching fold Acauses the membrane 16 to fold outwardly along the crease line 88. Thisfacilitates inward folding along the crease lines 104 and 106. Pinchingeach of the other folds C, E, B and D, in turn, enables the membrane 16to be similarly folded in the sectors in which those folds are located.The pinched folds may then be folded inwardly, one after the other,along the approximately circumferential fold line 28. The order of suchfolding may be the same as that in which they were pinched, that is, inthe order of A, C, E, B and D. With a first inward layer so produced,the appearance of the cone 10 is substantially the same as shown in FIG.5.

A substantially identical procedure may be followed for effecting theinward folding of the aft end of the cone in a second layer. Thus, asbest seen in FIG. 12, the folds for effecting this operation aredesignated by the letters F through J. Of these folds, only the fold Iis visible in FIG. 13. Pinching fold I causes the membrane 16 to foldoutwardly along the crease 68, as seen in FIG. 12. This facilitatesfolding of membrane 16 inwardly along the crease lines 96, 98 and 92,94. Here, again, folding of alternate ones of the folds is effected, inthe order of F, H, J, G and I, for example. Upon completion of suchfolding, the folds F through J may then be folded inwardly, one afterthe other, along the approximately circumferential fold line 34. Suchinward folding of the folds may be in the same order in which they werepinched. The appearance of the cone 10 with the second inwardly foldedlayer is substantially the same as shown in FIG. 4.

Folds for effecting the folding of the aft end of the cone 10 about theapproximately circumferential fold line 54 have been designated by theletters K through O in FIG. 12. Again, alternate ones of the folds, inthe order, for example, of K, M, O, L, and N, are effected, one afterthe other, by folding outwardly at creases 72 and 74 and inwardly at thecrease 108. Of these folds, only the folds N and O are visible in FIG.13. At an intermediate stage in this folding procedure, the appearanceof the cone 10 is substantially the same as shown in FIG. 3. Upon thecompletion of such folding, the extendible cone is in a collapsedcondition for stowage as illustrated in FIG. 2 and with the aft endthereof appearing as shown in FIG. 7.

For convenience, the foregoing manner of inward folding of theextendible exit cone is referred to herein as "axi-symmetrical" folding.

In FIG. 14 there is shown a schematic drawing illustrating certainrelationships of the nozzle extension cone 10 according to thisembodiment of the invention described in connection with FIGS. 2-13 andwhich distinguish significantly from corresponding relationships, asdescribed hereinbefore, in connection with the prior art representationof FIG. 1. By reference to FIG. 14, it will be seen that since themeridian length L_(s) is stowed in multiple layers, the length L_(s) maybe much larger than the radius R_(f) at the exit opening of the portionof cone 10, designated 50, that is not folded. This portion, as seen byreference to FIG. 8, is that portion between the forward cut off 52 ofmembrane 16 and the third approximately circumferential fold linedesignated 54. It is noted, that if desired, L_(s) may be larger thanR_(e), the radius at the exit plane 18 of the extendible cone 10. Asdescribed hereinbefore in connection with the prior art representationof FIG. 1, the length L_(s) of the prior art cannot exceed R_(f).

In FIG. 15 there is depicted, in a fragmentary view, a section of thefolded cone extension 10 with a trapped supporting system 112 for theattachment thereof to a rocket motor 12'. Specifically, a forwardportion 114 of the extendible cone 10 is trapped between the outer aftsurface 116 of the cone of a submerged nozzle 14' of the rocket motor12' and an annular conical band of plastic insulation 120. Surroundingthe annular band of insulation 120 is an annular titanium closure 122having an inner surface 124 that fits snugly over the outer surface ofthe plastic band 120. Titanium closure 122 is attached to an aftwardlyprojecting rim 123 of the rocket motor case 133 by a plurality ofsuitably circumferentially spaced bolts 125.

For supporting the cone extension 10 in a proper positional relationshipwith respect to the cone of the rocket motor nozzle 14', there isprovided a five-sided plastic ring 126. Plastic ring 126 desirably maybe made in four separate sections for facilitating the assembly of thetrapped supporting system 112. On the aft side thereof, as seen in FIG.15, the plastic ring 126 is in abutting relationship with the annularband of plastic insulation 120 and the closure 122. On the forward sidethereof, the five-sided plastic ring 126 is in abutting relationshipwith an annular shoulder 128 on the rocket motor cone 118. A titaniumring 130 having a circumferential groove 132 is slipped over adjacentcircumferential surfaces of the titanium closure 120 and the plasticring 126. An O-ring 134 which may be made of rubber or other suitableelastomeric material is provided in the groove 132 for sealing theinterface between the rocket motor case 133 and the assembly 112. Anannular plastic band 136 may be attached by a suitable adhesive to theadjoining surfaces of the rocket motor cone 118, plastic ring 126 andtitanium ring 130.

The membrane 16 employed in the fabrication of the extendible nozzlecone 10 may be made of any suitable ductile, heat and erosion resistantmetal or alloy. Metal alloys preferred for this construction are:

Columbium 10% Hafnium

Columbium 10% Tungsten 10% Hafnium 0.1% Yttrium (melting pointapproximately 4350° F.)

Tantalum 10% Tungsten (melting point approximately 5500° F.)

Each of these metal alloys is available in sheet stock. In 0.005 inchthickness, the weight of the first Columbium-based sheet is equivalentto about 0.033 inch 2D carbon-carbon and the weight of thetantalum-based sheet is equivalent to about 0.058 inches of 2Dcarbon-carbon (the term 2D meaning two-dimensional).

In FIGS. 16-18 there are illustrated methods and apparatus by means ofwhich the improved extendible nozzle exit cone according to theinvention may be fabricated as an integral, seamless, free-standingshape.

Thus, in FIG. 16 there is illustrated the spinning of an integral,seamless, free-standing nozzle exit cone 142 from a sheet blank or disc140 (shown in dotted lines) of refractory metal or other heat resistantmaterial, for example, an alloy of Columbium, as previously described,on a mandrel 144 having the shape of the frustum of a cone. The disc 140is held in a lathe between the conical mandrel 144 and a rotatingtailstock 146. The mandrel 144 may include, as shown, an integral flange148 to permit bolting thereof to the headstock (not shown) of the latheand a boss 150 of suitable diameter that fits into the headstock. Thedisc 140 is worked by means of force applied by opposed spinning wheels151 and 152 against the outer surface thereof, that is to say, againstthe surface adjacent the tailstock 146, as shown. While shown as beingperformed with the mandrel 144 spinning about its axis in a horizontalposition, it will be understood that the operation may be performed, ifdesired, with the mandrel 144 spinning about its axis in a verticalposition. Upon completion of the spinning operation, the central sectionof the formed cone 142 may be cut out to complete the formation of theextendible nozzle exit cone.

The mandrel 144 preferably is made of a dimensionally stable, hard, wearresistant material such as tool steel, and may be characterized inhaving somewhat different half-angles in successive sectionscorresponding to the regions between fold lines 28, 34 and 54 in FIGS.8, 12 and 13. By way of example, the region between the large diameterend and fold line 28 may have a half angle of 17° while the regionbetween fold lines 28 and 34 may have a half angle of 19°, the regionbetween fold lines 34 and 54 may have a half angle of 21°, and theregion between fold line 54 and the small diameter end may have a halfangle of 23°.

More than one mandrel 144 of progressively deeper contour may berequired in the formation of the extendible nozzle exit cone 142. Also,the refractory or other metal or disc 140 being worked may requireprocess annealing between operations to overcome work hardening.

A subsequent step in this method of fabricating the improved extendiblenozzle exit cone involves the transfer of the fold line patterns shownin FIGS. 8, 12 and 13 using suitable die presses installing within oroutside the seamless cone obtained as shown in FIG. 16. From this point,fabrication proceeds as described for the welded workpiece.

In FIG. 17, there is illustrated a method of fabricating the improvedextendible nozzle exit cone as an integral seamless, free-standing shapewhich involves the condensation of refractory metal or other material orcompounds thereof from the gaseous or vapor state to form solidstructural deposits on a conical mandrel 154. This process utilizes agaseous compound of the element to be deposited, for example, an alloyof Columbium, as previously described, or other refractory metals ormaterials such as Molybdenum, Rhenium, Tantalum and Tungsten.

As shown in FIG. 17, mandrel 154 is positioned in a reaction enclosureor chamber 156 which is connected by a conduit 158 to a source (notshown) of vacuum pressure for the evacuation thereof. Reaction chamber156 is provided to isolate the mandrel 154 in a controlled environment.Chamber 156 may include therein a turn table or holder 160 forsupporting and rotating the mandrel 154. This mandrel 154 may be afigure of revolution like the mandrel shown in FIG. 16 or may becharacterized as shown in FIG. 17 such that its surface represents thepartially folded improved extendible nozzle exit cone. The chamber 156further includes therein a gaseous reducing agent chamber 162 for therefractory metal, designated 164, to be deposited, and a source (notshown) of gaseous agent such, for example, as hydrogen or chlorine, thatis connected to chamber 162 by a conduit 166. By way of example, and notlimitation, it is noted that when the refractory metal is Rhenium thegaseous agent may be chlorine. Additionally, an induction heating coil168, energized from a suitable source of alternating electrical current(not shown) is provided externally of the reaction chamber 156 forheating the mandrel 154.

In the chemical vapor deposition apparatus of FIG. 17, chlorine or othersuitable gas is passed through the chamber 162. The refractory metal 164in chamber 162 preferably is in pellet form. When heated to a suitablyhigh temperature (by means not shown) there is a reaction between themetal and the chlorine gas. This reaction, when the refractory metal isRhenium, for example, forms a gaseous mixture of Rhenium pentachlorideat a temperature of about 500° C. Since the reaction is exothermic, thechamber 162 needs only initial heating to start the reaction, the heatproduced by the reaction being sufficient to sustain the reaction.

As the gaseous mixture passes over the heated mandrel 154, decompositionthereof takes place resulting in the deposition on the surface of themandrel 154 of the Rhenium metal as a metallic coating 170 and therelease of the chlorine gas which is evacuated from chamber 156 throughconduit 158.

A requirement of the mandrel 154 is that it be fabricated of a materialthat is dimensionally stable and will withstand the high depositiontemperature involved in the chemical vapor deposition process, and whichhas a temperature coefficient of expansion compatibility with thedeposited material or coating 170. Such compatibility is required to theend that upon cooling to room temperature there is no cracking ordeformation of the coating 170.

It is noted that in the fabrication of the improved extendible nozzleexit cone by the chemical vapor deposition process of FIG. 17, thefinished cone on the inside surface thereof will be an inversereproduction of the outside surface of the associated mandrel. Theoutside surface of the cone, however, particularly when thin, as isdesired for the extendible nozzle exit cone, will be a substantiallyexact reproduction of the outside surface of the associated mandrel.Thus, there may be formed in the finished extendible nozzle exit conethe crease lines necessary for enabling the multiple inward folding fromthe larger diameter, as described hereinbefore.

In order to control the uniformity of the thin coating for theextendible nozzle exit cone 170 in the process of FIG. 17, the chemicalvapor deposition process may be interrupted and the mandrel 154 may beturned upside down. This positions those portions of the mandrel 154 andthe coating 170 thereon which previously had been furthest from thegaseous reducing agent chamber 162 closer thereto, thus tending to makemore uniform the thickness of the coating 170 that is deposited on themandrel 154.

The chemical reactions involved in the chemical vapor deposition processand the thermal decomposition process taking place that results in thedeposition of coating on the surface of mandrel 154 of other refractorymetals such as Columbium, Molybdenum, Tantalum and Tungsten are known tothose skilled in the art, and therefore, will not be further describedherein.

In FIG. 18 there is illustrated another method of fabricating theimproved extendible nozzle exit cone according to the invention as anintegral seamless, free-standing shape which comprises electroplating athin layer or coating of a refractory metal or other heat resistingmaterial on a mandrel 172 similar to the figure of revolution mandrel ofFIG. 16 or the characterized mandrel of FIG. 17. Mandrel 172, as shown,is employed as the cathode in an electrolytic bath 174 contained in asuitable container 176, which bath may be composed of a solution of asalt of the refractory metal or other material being plated. The otherterminal or anode 178 in the electrolytic bath 174 may be made of thesame refractory or other material being plated, or if desired, may bemade of a chemically unaffected electrical conductor. When the anode 178is made of the same material as that being plated on the mandrel 172, itis noted that the electrolytic bath need not comprise a salt of themetal being plated although such may be desirable.

A low voltage direct electrical current is passed through the solution174 which electrolyzes and plates the cathodic mandrel 172 with therefractory metal or other material to a desired thickness. Only a lowvoltage is required for this operation because of the excellentconducting properties of a metallic salt solution. Typically, thevoltage may be of the order of six volts.

By way of example and not limitation, the mandrel 172 may be made ofcarbon with ridges and grooves formed as the surface thereof whichcorrespond to those desired to be formed on the surface of the finishedthin extendible nozzle exit cone, in the region of the larger diameter.In FIG. 18 the metallic coating or cone being built up on the mandrel172 is indicated by the reference numeral 180. Uniformity in thethickness of the cone 180 may be promoted by mounting the mandrel 172,as shown, on a turn table 182 that is suitably supported in thecontainer 176. If necessary to control the thickness of the coating 180,the electrolytic process may be interrupted and the mandrel 172 turnedupside down, or portions of the surface may be masked to halt furtherbuild-up while deposition continues on other portions thereof.

When the cone 180 has been built up to a desired thickness, the mandrel172 may be removed from the bath 174 and the carbon mandrel removed toleave the desired cone 180 of refractory metal or other material.

The mandrel 172 may be fabricated, if desired, from a material otherthan carbon, for example, from copper in which the formation of theridges and grooves in the surface of the mandrel may be more easilyeffected than in carbon. Upon completion of the electroplatingoperation, the copper mandrel may be dissolved or otherwise cut away toleave the desired extendible nozzle exit cone.

With reference to the mandrels 144, 154, and 172 of FIGS. 16-18,respectively, it will be understood that, if desired, the ridges andgrooves may be omitted therefrom and the necessary crease lines in thecone for enabling the multiple inward folding thereof may be madetherein following the cone forming process by suitably shaped brakepress or die press machines, as described hereinbefore.

In summary, it is noted that each of the embodiments of the inventionherein disclosed permits a sufficient amount of membrane material toproduce a very large area ratio at the exit plane to be stowed in a muchreduced envelope in comparison with the prior art. Thus, as shown inFIG. 1 which represents the prior art, since the length, L_(s), alongthe meridian of the extendible cone, cannot exceed the radius, R_(f), atthe region of attachment of the extendible cone to the rocket motornozzle, the length L_(a) along the longitudinal axis of the extendiblecone must be smaller than the length L_(s).

With the present invention, as represented by the schematic drawing ofFIG. 14, it will be seen that since the length L_(s) is stowed in manylayers, the length L_(s) may be much larger than the radius R_(f) at theregion of attachment of the extendible cone to the rocket motor nozzle,or even larger than the radius R_(e) at the exit plane of the extendiblecone.

In the illustrated embodiments of the invention, because of the reducedlength of the forward portion of the cone, and because the stowed aftportion maintains the shape at the interface, the stowed form of thecone 10 is quite rigid. Without such rigidity, the membrane exit cone isnot usable at all because it is too flimsy prior to motor ignition.

Because the required stiffness of the non-folded exit cone membrane isdetermined by pre-use inertia loading (i.e., prior to the development ofinternal pressure which stiffens the structure during use), theinvention makes possible the use of thinner, hence lighter, exit conemembranes than would otherwise be possible. Thus, the maximum achievableexit diameter that is practicable (before weight increase requires agreater increase of impulse than the area ratio permits) is made larger.

With this description of the invention in detail, those skilled in theart will appreciate that modifications may be made to the inventionwithout departing from its spirit. Therefore, it is not intended thatthe scope of the invention be limited to the specific embodimentsillustrated and described. Rather, it is intended that the scope of theinvention be determined by the appended claim.

What is claimed is:
 1. A rocket motor extendible nozzle for attachmentto a rocket motor nozzle having a throat area for increasing the ratioof the effective rocket motor nozzle/extendible nozzle exit coneeffective area to the rocket motor nozzle throat area comprising:anarcuate-shaped membrane (16) of ductile heat resistant material, saidmembrane (16) having opposed arcuate edges (51, 52) one (51) of which islonger than the other (52) having ends (46, 48) that are adapted to bebrought into edge-to-edge relationship to form a frustum of a cone,(10), the membrane portion forming that aft end of said frustum of acone being deformed by a plurality of cooperating crease lines of firstand second sets, each of the crease lines of said first and second setshaving an apex, with the apex of each of the crease lines of the firstset (28, 54, 62, 64, 68, 72, 74, 78, 80, 82, 84, 86, 88) pointing at theviewer from the exterior of the membrane when formed into a frustum of acone (10) and the apex of each of the crease lines of the second set(90, 92, 94, 96, 98, 100, 102, 104, 106) pointing away from the viewer,the crease lines of said first set running both circumferentially andlongitudinally of said frustum of a cone (10) and the crease lines ofsaid second set running longitudinally only thereof, with the creaselines that run circumferentially forming a plurality of fold lines (28,34, 54) that are approximately equidistant from each other, the foldline (28) closest the larger diameter end (51) of the cone beingsubstantially the same distance therefrom as from the fold line (34)adjacent thereto, whereby said frustum of a cone (10) may be foldedinwardly, axi-symmetrically thereof, in multiple layers from the aft endfor compact stowage relative to said rocket motor, and whereby saidextendible nozzle may be unfolded to the extended position thereof by aforward-to-aft flow of rocket motor gas therethrough upon firing of saidrocket motor.
 2. A rocket motor extendible nozzle as specified in claim1 wherein said membrane is formed of an alloy comprising Columbium and10% Hafnium.
 3. A rocket motor extendible nozzle as specified in claim 1wherein said membrane is formed of an alloy comprising Columbium, 10%Tungsten, 10% Hafnium and 0.1% Yttrium.
 4. A rocket motor extendiblenozzle as specified in claim 1 wherein said membrane is formed of analloy comprising Tantalum and 10% Tungsten.
 5. A rocket motor extendiblenozzle as specified in claim 1 wherein said membrane is formed ofMolybdenum.
 6. A rocket motor extendible nozzle as specified in claim 1wherein said membrane is formed of an alloy of Molybdenum.
 7. A rocketmotor extendible nozzle as specified in claim 1 wherein the deformationof said membrane by said cooperating crease lines of first and secondsets is in a pattern that is repeated in each of at least foursubstantially equal sectors into which said arcuate-shaped membrane isdivided.
 8. A rocket motor extensible nozzle for attachment to a rocketmotor nozzle having a throat area for increasing the ratio of theeffective rocket motor nozzle/extendible nozzle exit cone effective areato the rocket motor nozzle throat area comprising:an arcuate-shapedmembrane (16) of ductible heat resistant material, said membrane havingopposed arcuate edges (51, 52) one (5I) of which is longer than theother (52) and having ends (46, 48) that are adapted to be brought intoedge-to-edge relationship to form a frustum of a cone (10), the membraneportion forming the aft end of said frustum of a cone being deformed bya plurality of cooperating crease lines of first and second sets, eachof the crease lines of said first and second sets having an apex withthe apex of each of the crease lines of the first set (28, 54, 62, 64,68, 72, 74, 78, 80, 82, 84, 86, 88) pointing at the viewer from theexterior of the membrane when formed into a frustum of a cone (10) andthe apex of each of the crease lines of the second set (90, 92, 94, 96,98, 100, 102, 104, 106) pointing away from the viewer, the crease linesof said first set running both circumferentially and longitudinally ofsaid frustum of a cone (10) and the crease lines of said second setrunning longitudinally only thereof, wherein the deformation of saidmembrane by said cooperating crease lines of first and second sets is ina pattern that is repeated in each of at least four substantially equalsectors (60) into which said arcuate-shaped members (16) is divided,wherein creases of the first set form fold lines (28, 34, 54,) that areapproximately concentric with the arcuate edges (51, 52) of said members(16), the first one (28) of said fold lines (28, 34, 54) being closestto the longest arcuate edge (51) of said membrane (16), the third one(54) of said fold lines (28, 34, 54) being closest to the shortestarcuate edge (52) of said membrane (I6), and the second one (34) of saidfold lines (28, 34, 54) being approximately equidistant from said first(28) and third (54) fold lines, the width of the regions between theexit plane (18) and the first (28) fold line, the first (28) and second(34) fold lines and the second (34) and third (54) fold lines beingapproximately the same, the second one (34) of said fold linescomprising two creases (62, 64) which meet at a small angle to eachother at substantially an intermediate output (66) across the width ofthe sensor (60) and overlap into adjacent sectors, others (68, 72, 74)of said creases of said first set connecting the junction (66) of thecreases of said second (34) fold line to a midpoint (70) of the sectoron the first (28) fold line and the ends of said third (54) fold line,still others (78, 80, 82, 84) of said creases of said first setconnecting a central point (76) on the longest arcuate edge (51) of thesector (60) to the ends of said first fold line (28) and to pointsthereon intermediate the center and the ends of said first (28) foldline, others (86, 88) of said creases of said first set connecting theends of said first (28) fold line to said longest arcuate edge (51) ofsaid sector (60), said creases of said second set (90, 92, 94, 96, 98,100, 102, 104) connecting said central point (76) on the longest arcuateedge (51) of the sector (60) to a central point (70) on said first (28)fold line and connecting said longest arcuate edge (51) from a pointadjacent each side of the sector (60) to the ends of said first (28)fold line and connecting the junction (66) of the creases of said secondfold line to the ends of said first (28) fold line and the pointsthereon intermediate the center (70) and the ends thereof, whereby saidfrustum of a cone (10) may be folded inwardly, axi-symmetricallythereof, in multiple layers from the aft end for compact stowagerelative to said rocket motor, and whereby said extensible nozzle may beunfolded to the extended position thereof by a forward-to-aft flow ofrocket motor gas therethrough upon firing of said rocket motor.
 9. Arocket motor extendible nozzle for attachment to a rocket motor nozzlehaving a throat area for increasing the ratio of the effective rocketmotor nozzle/extendible nozzle exit cone effective area to the rocketmotor nozzle throat area comprising:a membrane (16) of heat resistantmaterial formed in the shape of a frustum of a cone (10) with a portionthereof at the aft and larger radius end deformed by a plurality ofcrease lines of first and second sets in a pattern that is repeated inat least each of four substantially equal sectors (60) of the surface ofsaid frustum of a cone (10), each of the crease lines of said first andsecond sets having an apex, with the apex of each of the crease lines ofthe first set (28, 54, 62, 64, 68, 72, 74, 78, 80, 82, 84, 86, 88)pointing at the viewer from the exterior surface of the membrane and theapex of each of the crease lines of the second set (90, 92, 94, 96, 98,100, 102, 104, 106) pointing away from the viewer with some of thecrease lines of said first set and all of the crease lines of saidsecond set running longitudinally of said cone with others of the creaselines of said first set running circumferentially of said cone to form aplurality of fold lines that are approximately equidistant from eachother, said crease lines of said first and second sets cooperating witheach other to the end that said frustum of a cone may be foldedinwardly, axi-symmetrically thereof, in multiple layers, from the aftand larger radius end thereof for stowage relatively to said rocketmotor, and to the end that said folded cone may be unfolded to theextended position thereof by a forward-to-aft flow of rocket motor gastherethrough upon firing of said rocket motor.
 10. A rocket motorextendible nozzle as defined by claim 9 wherein said frustum of a coneis formed as an integral seamless, free-standing shape.
 11. A rocketmotor extendible nozzle for attachment to a rocket motor nozzle having athroat area for increasing the ratio of the effective rocket motornozzle/extendible nozzle exit cone effective area to the rocket motornozzle throat area comprising:a membrane (16) of heat resistant materialformed in the shape of a frustum of a cone (10) with a portion thereofat the aft and larger radius end (51) deformed by a plurality of creaselines of first and second sets in a pattern that is repeated in at leasteach of four substantially equal sectors (60) of the surface of saidfrustum of a cone (10), each of the crease lines of said first andsecond sets having an apex, with the apex of each of the crease lines ofthe first set (28, 54, 62, 64, 68, 72, 74, 78, 80, 82, 84, 86, 88)pointing at the viewer from the exterior surface of frustum of a cone(10) and the apex of each of the crease lines of the second set (90, 92,94, 96, 98, 100, 102, 104, 106) pointing away from the viewer within thecrease lines in the surface of said frustum of a cone of said first set(54, 62, 64, 68, 72, 74, 78, 80, 82, 84, 86, 88) run bothcircumferentially and longitudinally with respect thereto and the creaselines of said second set (90, 92, 94, 96, 98, 100, 102, 104, 106) runlongitudinally only with respect thereto, with the crease lines of saidfirst and second sets cooperating with each other to the end that saidfrustum of a cone (10) may be folded inwardly, axi-symmetricallythereof, in multiple layers, from the aft and larger radius end thereoffor stowage relatively to said rocket motor, and to the end that saidfolded cone may be unfolded to the extended position thereof by aforward-to-aft flow of rocket motor gas therethrough upon firing of saidrocket motor.